Method for refining antimony by electrolysis of acid electrolytes



Patented" Nov. 11, 1930 UNITED STATES .IP'ATENT- OFFICE.

EEINRICH ROSCEER, OF HAMBURG, GERMANY, ASSIGNOR TO NORDDE'U'TSCHE.

e AFFINERIE, OF HAMBURG, GERMANY METHOD FOR REFINING ANTIMONY BY ELECTROLYSIS OF ACID ELECTROLYTES 1T0 Drawing. Applicatipnfiled October 5, 1927,v Serial No. 224,279, and in Gerinany July 18, 1927..

This invention relates to a method for refining antimony by electrolysis of acid electrolytes.

v A crude antimony, which is adapted for 5 'electrolytical purposes, may co'ntain lead, tin, iron, nickel, zinc, copper, bismuth, silver and gold besides other more rare impurities. Of-

greater practical importance is the fact, that greater amounts of lead for example 5% o and tin for example 8% and more may be present in the crude antimony without disturbing the electrolysis. has to be removed from the crude antimony by remelting it with alkali.

According to the invention the refining of crude antimony is carried through by electrolyzing electrolytes containing antimony tri-fluoride, in which a .considerable excess of free sulphuric acid and small amounts of free hydrofluoric acid are maintained. When using such electrolytes the deposition of d1s-.

turbing basic antimony salts upon the anode is avoided.

It has already been proposed to use electrolytes containing antimony trifluoride for the electrolytical refining of crude antimony. A very detailed description of this method is to be found in the Transactions of the American Electrochemical Society, vol. 28, 1915, page 325. There however it is stated,

that the electrolyte should be absolutely free from sulfuric acid. It is further stated thatlead present in the anodes goes over into the cathodes. The antimony electrolytically deposited upon the cathodes contained for-example O.35% Pb and was therefore of 111- ferior quality.

According to the present invention the above described difiiculties are avoided, when using an electrolyte containing a considerable excess of free sulfuric acid for example 60- 600 gr. H SO perliter and a small amount of free hydrofluoric acid for example 20 gr. HF per liter. With such a strongly acid solution a clogging of the anode by precipit'ated basic antimony sulfate is avoided and by the great excess of sulfuric acid the solubility of the lead in the electrolyte is so much reduced, that it cannot enter the cathode. An

! electrolyte containing the antimony tri- Arsenic howeverfluoride in a strong sulfuric acid solution is well adapted for the electrolysis of even very impure antimony with best results. The pure metal obtained contains 99.8% Sb. Difliculties at the anodes donot occur and the electrolyte "is comparatively cheap, as it allows to operate with a minimum ofhydrofluoric acid.

For the preparation of the electrolyte pulverized crude antimony is boiled with concentrated sulfuric acid in kettles of cast iron, until the development ofsulfur dioxide stops.

For example 100 kg. antimony are boiled with 250 kg. sulfuric acid B. The pasty massobtained contains much free sulfuric acid andhydrofluoric. acid is added, whereby the antimony is at once dissolved, as antimony is added. An upper limit for the content of free sulfuric acid is not given, as electrolytes containing300 and even 600 gr. H SO, per liter may be used with satisfactory results.

The electrolysis is carried through in vessels with lead lining. It is not necessary to heat the electrolyte; heating would only lead to losses of hydrofluoric acid. The anodes are cast plates of crude antimony withcopper ears for suspending them. The cathodes are for example copper plates, from which the pure antimony deposited. may be easily removed. In some cases one may'replace the foregoing acids by other ingredients, but I have found such substitutions not to be as satisfactory. For example, one may replace the free sulphuric acid by alkali-bisulphate and the free hydrofluoric acid by a mixture of alkali-fluoride and free sulphuric acid.

The waste electrolytes may e easily worked up for their content of free hydrofluoric acid.

- For this purpose the metals precipitable from ing impurities such; as lead insoluble therein, said electrolyte being of a character such as to prevent said anode from becoming passive, and electrolyzing the electrolyte to deposit antimony substantially without the deposition of the lead therewith.

In testimony whereof I'aflix my signature.

' HEINRICH ROSCHER.

containing antimony trifluoride, a consider able excess ofa substance containing the radical HSO and a small excess of HF introducing thereinto an anode soluble at least in part in said electrolyte and containing impurity substantially insoluble therein, said electrolyte being of a character such as to prevent said anode from becoming passive,

and electrolyzing" the solution to deposit antimony without the deposition of the im:

purity therewith.

2. A process for refining crude antimony which comprises preparing an electrolyte with antimony trifluoride containing a considerable excess of free s'ulfuric'acid and a small excess of tree hydrofluoric *acid,introducing thereinto an anode soluble in said electrolyte containing impurities such as'lead,

said electrolyte being of a character such as and electrolyzing the electrolyte to deposit antimony substantially without the deposition of the lead therewith.

3. A process for refining crude antimony I which comprises reparing an electrolyte siderable excess of free-sulfuric acid and a small excess of free hydrofluoric acid introto preventsaid anode from becoming passive,

with antimony tri uoride containing a conducing thereinto an antimony anode soluble in said electrolyte and containing impurities such as lead insoluble therein, said electrolyte bein of the character such as to prevent said ano e from becoming passive, and electrolyzing the electrolyte to deposit antimony substantlally withontthe deposition of the grams free. sulfuric acid lead therewith.

+1 A process of refining-crude antimony which comprises preparing an electrolyte with antimony trifluoride containing at least er liter and a small amount of free hydro uoric-acid, introduclng thereinto an antimony anode 'solu- 'ble in said electrolyte and contalmng impurities such as lead insoluble therein, said elecharacter such as to prevent trolyte being 2f a c m becoming paxive, and elecsaid anode. trolyzing substant ally without the deposition of the impurities therewith. v

electrolyte to deposit antimony 5. A process -of refining crude antimony which comprises with antimonytri grams free sulfuric acid per liter and about. 20 grams free hydrofluoric acid per liter, introducing thereinto an antimony greparing an electrolyte uoride containing about anode soluble in said electrolyte and contain- 

